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Effect of extra-framework Al formed by successive steaming and acid leaching of zeolite MCM-22 on its structure and catalytic performance

Paper ID Volume ID Publish Year Pages File Format Full-Text
41163 45879 2012 11 PDF Available
Title
Effect of extra-framework Al formed by successive steaming and acid leaching of zeolite MCM-22 on its structure and catalytic performance
Abstract

Dealuminated MCM-22 samples have been prepared by a two-step dealumination procedure. Detailed assessment of the properties of the materials obtained at each one of the successive stages, i.e. steaming (at 500 °C, 700 °C and 800 °C) and acid reflux (HCl and oxalic), has been made by XRD, N2 adsorption–desorption, m-xylene adsorption, 27Al MAS NMR and FT-IR of pyridine adsorption. It was found that steaming generates extra-framework aluminum (EFAl) species and the majority of them cannot be extracted by the consecutive acid leaching. These extra-lattice entities block the zeolite micropores which makes the remaining Broensted acid sites isolated and inefficient. It is shown that the presence of such species vastly affects the catalytic performance of zeolite MCM-22 in the reaction of m-xylene conversion. The consequences are reduced adsorption capacity and catalytic activity, modified reaction products distribution, enhanced p-xylene selectivity, as well as altered mode of coke formation and composition of the coke precursors.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (197 K)Download as PowerPoint slideHighlights► Extra-framework Al (EFAl) species remain captured in steam-acid dealuminated MCM-22. ► EFAl blocks the micropores and makes the acid sites isolated and inefficient. ► Reduced adsorption capacity and catalytic activity in m-xylene conversion. ► Enhanced p-xylene selectivity and change in coke composition.

Keywords
MCM-22 zeolite; Steam-acid dealumination; Extra-framework Al; m-Xylene conversion; Coke formation
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Effect of extra-framework Al formed by successive steaming and acid leaching of zeolite MCM-22 on its structure and catalytic performance
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volumes 417–418, 29 February 2012, Pages 76–86
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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